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Yak-50, G-YAKK

Summary:

The aircraft was on a local flight from Carlisle Airport when the engine failed due to loss of oil pressure. The windscreen became partially obscured with an oil film but the pilot was able to make a forced landing in a field, during which the aircraft was substantially damaged. He vacated the aircraft unaided, but later attended hospital as his injuries became more apparent. On examining the engine, the pilot identified that the oil pressure adjustment valve was missing from the oil scavenge pump housing (Figure 1). It was found in the lower cowling with no evidence of the expected wire locking. He believed that the valve had worked loose and fallen out during the accident flight, causing the oil loss. The aircraft had recently undergone extensive maintenance which included an overhaul of the oil scavenge pump assembly. Initial flights following this work revealed a small oil leak in the area of the pump, which at the time, was thought to be have been remedied by an engineer tightening the small vertical bolts adjacent to the pressure adjustment valve.